Welcome to the Asana Forum 
You can do that with shortcuts already. After you realise you have just archived the wrong notification hit the following keys in this order:
| Step Nr. | Keystroke | Action |
|---|---|---|
| 1. | S | → gets you into the Archive |
| 2. | U | → unarchives the selected notification |
| 3. | H | → gets you back to the Inbox |
You can also select other notifications with ↓ and ↑ arrows.
Once you hit this sequence a couple of times, you’ll get used to it and it’ll be as quick as a CTRL+Z.
Cheers,
Rosario